Climate and Smoke

Climate simply describes the prevailing weather of an area. Understanding climate patterns can help develop long-range smoke management plans or adapt short-range plans. For example, afternoon mixing heights in most coastal regions of the United States are typically lower than the interior because moist, marine air is relatively stable. This means that there may be fewer days with optimum dispersion along the coast than interior. It usually is windier along the coast, however, and burns might be scheduled in the early morning if offshore breezes are desired to reduce smoke impacts on cities and towns.

It is possible to infer climate just by local proximity to oceans, lakes, rivers, and mountains. Also, vegetation cover can give an indication of climate. Desert landscapes, with a lot of bare soil or sand, heat and cool rapidly, causing them typically to have high daytime mixing heights and very low nighttime mixing heights. Natural landscapes of lush green forests tend to absorb sunlight while transpiring moisture, both of which help to modify heating and cooling of the ground surface. This can reduce daytime mixing heights and keep nighttime heights relatively high, with respect to deserts. Also, the structural deformation of trees often indicates high winds, where the direction of branches or flagging point away from prevailing wind directions.

Quantitative summaries of climate can be obtained from the state climatologist or Regional Climate Center (RCC), many of whom also maintain informative Internet sites and can be reached through the National Climatic Data Center (NCDC). It is most common to find temperature and precipitation in climate summaries. Monthly or annual averages or extremes are readily available while climate summaries of daily data are just beginning to emerge. For example, a recently generated climate database by Ferguson and others (2001) provides information on twice-daily variations in surface wind, mixing height, and ventilation index over a 30-year period.

We know that there are year-to-year variations in climate (e.g., ENSO) so at least 10 years of weather data are needed to obtain a preliminary view of climate in a particular area. There also are natural, “decadal” patterns in climate that last from 7 to 20 years. Therefore, it is appropriate to acquire 30 to 50 years of weather observation data for any reliable climate summary.

See: Fire Climate in the Fire Weather section for more information.